Abstract: the present invention provides a method for authenticating a user in a multiparty quantum communication comprising: generating l quantum entangled states with N particles and transmitting each particle of the l quantum entangled states to N users, by a quantum communication server, wherein the N is a natural number larger than 2; determining, by the quantum communication server, whether a disguised attacker exists among N users on the basis of a first error rate calculated by using n quantum states randomly selected from the l quantum states possessed by the users respectively and a previously shared secret key in each of the users; and controlling, by the quantum communication server, each of the users to generate a new secret key using mk quantum states and replace the previously shared secret key with the new secret key.

Abstract: A method and system for performing a quantum bit commitment protocol is provided. The method of performing a quantum bit commitment protocol to send bit information from a first party to a second party includes a pre-commit phase to randomly select and send, by the second party, a quantum state to the first party; a commit phase to perform, by the first party, a unitary transformation on the quantum state to combine the bit information with the quantum state and send the unitary-transformed quantum state to the second party; a hold phase to hold the unitary-transformed quantum state for a predetermined time period; and a reveal phase to provide, by the first party, information about the unitary transformation to the second party to open the bit information to the second party. The reveal phase may include a verification process to check if the opened bit information matches the bit information committed in the commit phase.

Abstract: There is provided a quantum-key distribution method between a plurality of users or groups. A center prepares a predetermined number of entangled states consisting of qubits equal to the number of the users, and generates quantum states consisting of the qubits belonging to each of the entangled states and corresponding to each of the users. The center transmits each of the quantum states to each of the users after an authentication process. Each of the users receiving the quantum state makes public an axis used to measure each of the qubits constituting the quantum states. The number of users in each group measuring the qubits with a predetermined axis is represented by module 4. If the sum of the module 4 of each group is even, each group collects the qubit measurement results of the users and acquires each group key. Therefore, it is possible to provide a high-security quantum-key distribution method between an unspecified number of users or groups.